FIG. 13 illustrates an example of the configuration of a conventional production system.
The production system 101 performs various kinds of processing on a number of kinds of production elements (products) e1-e7 successively entered into the system, and includes an automatic machine process 80 as illustrated in FIG. 13.
Hereinafter, description will now be made in relation to an example of the configuration of the automatic machine process 80 with reference to FIG. 13.
The automatic machine process 80 processes the production elements e1-e7 and includes production lines A, B, and C.
Hereinafter, the reference numbers A, B, and C are used when one of a number of production lines needs to be discriminated from the remaining lines, but an arbitrary production line is represented simply by the word “production line” without using a reference number. In addition, the reference numbers e1-e7 are used when one of a number of production elements needs to be discriminated from the remaining elements, but an arbitrary production element is represented by the reference symbol “e”.
The automatic machine process 80 sorts production elements e entered into the automatic machine process 80 to any one of the production lines A, B, and C by the kinds of production elements e. In the example of FIG. 13, the production element e1 and the production element e4 are sorted into the production line A; the production element e2, the production element e5, and the production element e7 are sorted into the production line B; and the production element e3 and the production element e6 are sorted into the production line C in accordance with the kinds of production elements e.
In addition, each of the production lines A, B, and C is equipped with one or more automated machines 81a-81e. In the example of FIG. 13, the production line A is equipped with an automated machine 81a; the production line B is equipped with an automated machine 81b and an automated machine 81c; and the production line C is equipped with an automated machine 81d and an automated machine 81e. 
Hereinafter, the reference numbers 81a-81e are used when one of a number of automated machines needs to be discriminated from the remaining machines, but an arbitrary automated machine is represented by the reference number “81”.
An automated machine 81 processes a production element e. An operation process performed by the automated machine 81 consists of a number of unit processing steps (not illustrated) arranged in time series. The unit processing steps representing various steps (processing steps) performed in an automated machine 81 in units determined according to the contents of the processing steps, and includes manual steps, such as setup, performed by an operator and automatic steps representing processing automatically carried out by an automated machine 81.
Shares of the operation performed by respective operators X and Y are not clearly defined, and therefore each of the manual steps at automatic machines 81a-81e is carried out by either the operator X and Y.
In the automatic machine process 80, the operators X and Y split up to take over respective different manual steps.
Into such an automatic machine process 80, a number of production elements e1-e7 are successively input and are each processed in either one of the production lines A, B, and C. The production elements e that underwent processing are successively ejected out of the automatic machine process 80 to serve as processed product in the same order of into the automatic machine process 80.
In a typical automatic machine process 80, when operation processing steps of an automated machine 81 include a manual step, the next unit processing steps is not carried out in the automatic machine 81 until the operator finishes the manual step. Therefore, each of operators X and Y are required to efficiently carry out operation.
In order to efficiently carry out operation by a number of operators X and Y in an automatic machine process 80, there have been proposed various methods of notifying operators of instructions of manual steps that the operators should preferentially take over next.
For example, one of the methods recognizes manual steps and notifies operators of instructions of all the recognized manual steps and the preferential order of the manual steps.
Another method recognizes a bottleneck step and preferentially instructs the operators of operation at any production line and any automatic machine. Further, a method preferentially instructs the operators to carry out manual steps on elements entered into the system earlier on the basis of the principle of first-in first-out.
For example, the Patent Reference 1 below discloses a method in which a source terminal forwards, when an operation needs to be carried out, the operation contents, the preferential degree of the operation, the preferential of a test machine, and the preferential degree of a previously-entered to each terminal and each terminal instructs an test machine that is to carry out the operation, considering the preferential degrees.    [Patent Reference 1] Japanese Patent Application Laid-Open (KOKAI) Publication No. 2006-163889
However, in a mixed production in which a number of production elements e1-e7 without possessing regularity are entered into a production system and the entered production elements e1-e7 are successively processed, the combinations of the production elements e1-e7 currently in the automatic machine process 80 occasionally varies, so that a preferential operation, a preferential automatic machine and a preferential degree of a previously-entered are randomly changed. This is because the contents and the required time of a processing step vary with the kind of production element e.
Therefore, even when the above conventional methods are applied to such mixed production, it is problematically impossible to appropriately set the degree of preference of each manual step to be carried out by an operator.
In addition, since the operators X and Y does not clearly split up to take over operations, concurrent instructions of preferential order of manual steps to be varied out by the respective operators sometimes results in redundancy in operation.
In addition, the technique of the above Patent Reference 1 analyzes the preferential degrees on an assumption that a machines are operating at constant intervals and therefore has a difficulty in issuing operation instruction in which the result of analysis of operation that randomly occurs in mixed production is considered.